The longest recorded time without sleep is approximately 264 hours, or just over 11 consecutive days. Although it’s unclear exactly how long humans can survive without sleep, it isn’t long before the effects of sleep deprivation start to show.

After only three or four nights without sleep, you can start to hallucinate. Prolonged sleep deprivation can lead to:

Missing 24 hours of sleep isn’t uncommon. You might miss a night of sleep to work, cram for a test, or take care of a sick child. While it might be unpleasant to stay up all night, it won’t have a significant impact on your overall health.

Still, missing a night of sleep does affect you. Studies have compared 24-hour wakefulness to having a blood alcohol concentration of 0.10 percent. This is above the legal limit to drive in most states.

Some effects of going 24 hours without sleep include:

drowsiness

irritability

impaired decision-making

impaired judgement

altered perception

memory deficits

vision and hearing impairments

decreased hand-eye coordination

increased muscle tension

tremors

increased risk of accidents or near misses

Symptoms of 24-hour sleep deprivation usually go away once you’ve had some shut-eye.

Staying awake for just 36 hours can have intense effects on your body.

Your sleep-wake cycle helps regulate the release of certain hormones, including cortisol, insulin, and human growth hormone. As a result, going without sleep for an extended period of time can alter several bodily functions.

After two nights of missed sleep, most people have difficulty staying awake. They might experience periods of light sleep that can last up to 30 seconds. During these “microsleeps,” the brain is in a sleeplike state. Microsleeps happen involuntarily. After a microsleep, you might feel confused or disoriented.

Staying awake for 48 hours also disrupts the immune system. Inflammatory markers, which help your body prevent and target illnesses, start to circulate at increased levels. Some research has shown that natural killer (NK) cell activity decreases with sleep deprivation. NK cells respond to immediate threats to your health, such as viruses or bacteria.

After 72 hours without sleep, most people experience an overwhelming urge to sleep. Many are unable to stay awake on their own.

Going three days without sleep profoundly limits the ability to think, especially executive functions such as multitasking, remembering details, and paying attention. This level of sleep deprivation can make it difficult to see even simple tasks through to completion.

Emotions are also affected. People who have undergone this level of sleep deprivation may be easily irritated. They may experience a depressed mood, anxiety, or paranoia. Research has also found that sleep deprivation makes it more difficult to process others’ emotions. In one study, participants with 30 hours of sleep deprivation had difficulty recognizing angry and happy facial expressions.

Finally, several days of sleep deprivation can significantly alter perception. You might experience hallucinations, which occur when you see something that isn’t there. Illusions are also common. Illusions are a misinterpretation of something that’s real. An example is seeing a sign and thinking it’s a person.

Sleep deprivation can change both your appetite and the types of foods you crave. Studies suggest that sleep deprivation is associated with both an increased appetite and an increased desire for foods associated with weight gain. However, consuming empty calories can ultimately leave you more tired.

Eating well may offset some of the effects of sleep deprivation, but only to an extent. Since your body is conserving energy, opt for lean, protein-rich foods, such as nuts and nut butters, cottage cheese, or tofu. Avoid fatty proteins, such as steak or cheese. These will make you sleepier.

Dehydration can exacerbate the effects of sleep deprivation — such as grogginess and difficulty concentrating — so it’s also important to drink plenty of water.

Chronic partial sleep deprivation is when you don’t get enough sleep on a regular basis. It’s different than pulling an all-nighter once in a while. It’s also more common than missing one or two nights of sleep in a row, as most people are likely to sleep for at least a few hours per night.

The Centers for Disease Control and Prevention (CDC) report that 35 percent of American adults don’t get enough sleep per night. Chronic partial sleep deprivation is associated with both short-term health risks and long-term complications.

Not getting enough sleep over a short period, such as a week, may cause:

anxiety

unstable mood

drowsiness

forgetfulness

difficulty concentrating

difficulty staying alert

cognitive impairments

decreased performance at work or school

increased risk of illness or injury

In the long term, not getting enough sleep can reduce immune functioning and increase your risk of certain health conditions. These include:

It isn’t clear how long humans can truly survive without sleep. But it is clear that extreme symptoms can begin in as little as 36 hours. This includes a reduced ability to think, poor decision-making, and speech impairment.

Pulling an all-nighter once every couple of months likely won’t do any long-term damage. But if they’re happening more often — intentionally or not — talk to your doctor.

If you’re staying awake out of necessity, your doctor may be able to offer advice on how to do so in the most health-conscious way. Otherwise, your doctor can get to the root of your symptoms and help you get your sleep schedule back on track.